Cryogenic tank support



p 5, 1967 M. A. SEGURA ETAL 3,339,782

CRYOGENIC TANK SUPPORT Filed Jan. 22, 1965 FIG. 1

FIG. 2

INVENTORS MARNELL A. SEGURA CHARLES D. FORMAN (40 v HAROLD 'R. PRATT PRESSURE I REG. WHELAN,CHASAN ,LITTON, MARX a WRIGHT ATTORNEYS United States Patent 3,339,782 CRYOGENIC TANK SUPPORT Marnell Albin Segura, Baton Rouge, La., and Charles D.

Forman, Elizabeth, and Harold R. Pratt, Ridgewood,

N.J., assignors to Esso Research and Engineering Company, a corporation of Delaware Filed Jan. 22, 1965, Ser. No. 427,257 2 Claims. (Cl. 220) ABSTRACT OF THE DISCLOSURE A unitary, insulated, cryogenic tank is supported by the piston rods of a series of dashpots arrayed thereabout and mounted to an external shell for controlled movement relative thereto. By careful control of the pressure in the dashpots, through suitable hydraulic or mechanical means, the insulated tank is maintained effectively unrestrained and will be free to be displaced in any and all directions when subjected to varying thermally induced stresses and to the dynamic forces encountered. Thus the new and improved free-floating support of a cryogenic tank substantially reduces the magnitude and potential deleterious effects of the stresses induced in both the tank structure and the supporting structure.

The present invention relates to tanks for cargo ships and the like, and more particularly, to improvements in tankers adapted to transport cryogenic cargoes, such as liquefied gases, at atmospheric pressures.

It has been established that the transportation of gases, such as natural gas, hydrogen, oxygen, methane, and the like, to remote locations, may best and-most efliciently be accomplished by reducing the volume of the gas through its conversion into the liquid state. Such a conversion enables the storage volume requirements to be greatly reduced (approximately six-hundredfold for a given quantity of methane gas, for example) and, as should be appreciated, enables the most efiicient transfer of the gas to a remote area.

In order to transfer liquefied gas in a practical and economical manner in relatively large volumes, it is necessary to store the liquefied gas at approximately atmospheric pressure, since large containers built to withstand superatmospheric pressures would be impractical, if not impossible, to construct for use on seagoing tankers or the like. However, liquefied gases maintained at atmospheric pressures have extremely low vaporization points, ranging from about 435 F. for liquefied hydrogen, to 28 F. for liquefied ammonia, and these unusually low temperatures of the liquids present certain problems in the design and production of insulated cargo containers. Specifically, the containers must be capable of preventing heat losses which would lead tosubsequent vaporization of the stored liquefied gas and of withstanding the internal stresses that may be induced therein by the large temperature gradient through the walls of the container. In addition, the ship must be safeguarded against uncontrolled fiow of the low temperature liquid into contact with parts of the structure which could be damaged thereby.

Accordingly, for the purposes of safety and reliability and in accordance with accepted regulatory codes, it has been a well-established practice to provide at least two liquid-tight barriers in containers used for the transportation and/or storage of liquefied natural gases at cryogenic temperatures, each of which barriers is possessed of suflicient strength to withstand the hydrostatic loads imposed by the liquefied gas cargo and each of which is capable of withstanding the thermally induced stresses of the supercooled liquefied natural gas cargo. To this end, containers 3,339,782 Patented Sept. 5, 1967.

accommodating contraction of the tank due to the severetemperature changes encountered in normal use.

In accordance with the principles of the present invention, the cargo tank and the insulation therefor, in the form of a unit, are isolated from the ships structure and floatingly supported within an independent, closed steel shell mounted in the hull of a ship. Specifically, the insu-- lated tank is supported by and through the piston rods of a series of dashpots arrayed thereabout and mounted to the shell for controlled movement relative thereto. By careful control of the pressure in the dashpots, through suitable hydraulic or mechanical means, the unitary insulated tank is maintained effectively unrestrained and will be free to be displaced in any and all directions when subjected to varying thermally induced stresses and to the dynamic forces encountered on a ship. By providing independent and non-constrained support of the tank, its structure will not be unduly stressed when subjected to the severe thermodynamic and hydrostatic forces of a cryogenic cargo. Similarly, the supporting structure, being independent of the tank and effectively isolated therefrom by the array of controllably displaceable dashpot mecha-,

nisrns, will be substantially free of induced stresses during the loading and unloading (chilling and warming) cycle of the insulated tank. Thus the new and improved, free-floating support of a cryogenic tank substantially re..

duces the magnitude and potential deleterious effects of the stresses induced in both the tank structure and the supporting structure.

For a more complete understanding of the present invention and its attendant advantages, reference should be made to the following detailed description taken in conjunction with the accompanying drawing, in which:

FIG. 1 is a fragmentary, cross-sectional view of a ship- Referring to FIG. 1 of the drawing, the new system is especially adapted for the marine transportation of liquefied natural gases and, as such, is shown in the contemplated environment of a ship hull -10. Specifically, steel support members 11 extend inwardly and parallel with the three major axes of the ship from the hull 10 and trans verse cofferdams or bulkheads 12, to support a steel inner shell 13. v

In the'illustrated preferred embodiment, a cryogenic cargo tank 15 comprises an innermost aluminum or stainless steel tank 16, constituting a primary vaporand liquidtight barrier, and an enveloping, impermeable layer of insulation 17 constituting a secondary vaporand liquidtight barrier. The tank assembly is floatingly supported, in accordance with the principles of the invention, for movement along its major axes vertically, horizontally, and/or transversely with respect to the ships structure. The insulation 17 is effectively unitary and may be composed of discrete panels appropriately interconnected to be continuous and liquid-tight.

Where the cargo tank includes at least two liquid-tight barriers, as is the case in the illustrated and preferred embodiment, the inner shell 13, itself, need not be constructed as a liquid-tight barrier. Of course, if the supported tank constituted only a primary barrier for the contained cargo,

it would be necessary for an additional or secondary barrier to be included between the cargo and the ship structure. This could be accomplished by making the shell, itself, impervious or by enveloping the shell with a liquidtight secondary barrier.

' More specifically, the side walls 18-21, bottom wall 22, and top wall (not shown) of the tank 15 have one or more spacing rods 25 suitably secured thereto by bolts 26 acting through integral flanges 25a and mounting plates 24 embedded in the insultation 17. In accordance with the inventive concepts, the distal end of each of the spacing rods 25 is in the form of a piston head 42 and is an integral part of a movable dashpot mechanism 27. As shown best in FIG. 2, the dashpot 27 includes a dashpot cylinder 28 appropriately mounted to the shell 13 in channels 30 for limited sliding movement relative thereto in the plane normal to the spacer element 25. The channels 30 are welded to the shell 13 adjacent enlarged openings 29 formed therein.

In accordance with the invention, each rod 25 possesses three degrees of freedom relative to the shell 13 or, in other words, is free-floating, since it is bi-directionally movable in the dashpot cylinder 28 and since it is movable in horizontal and vertical directions with the entire dash: pot cylinder, itself, in the general planes of the Walls of the shell 13. As will be appreciated, the dimensions of the channel 30, the openings 29, and the cylinder 28 controlling the stroke of the rod 25 will define the actual,

quantitative limits of each of the three degrees of freedom.

' As shown in FIG. 2, the inner end 32 of the dashpot cylinder may be urged into a sliding relation with the outer face of the shell 13 by biasing forces applied by a spring 33 acting inwardly against the outer end 34 of the dashpot cylinder 28 and outwardly against a disk 35 slidably associated with the channel 30. The outer end 34 of the dashpot cylinder has an orifice 36 therein to permit the admission of pressure fluid into the cylinder 28 through a pipe 38 which projects outwardly through openings 37 formed inthe channel 30. As shown, the openings 37 are of sufficient dimension to accommodate movement of the pipe 38 relative to the channel 30 during the horizontal or vertical sliding displacement of the dashpot therein.

In accordance with a more specific aspect of the invention, the pressure in the dashpots 27 and the forces acting inwardly against the piston 42 are controlled through av suitable fluid medium, for example, an inert gas such as nitrogen, by one or more external pressure regulators 40' comunicating with the cylinders 28, individually or in appropriate groups, through flexible conduits 41. Alternatively, the external forces applied to the dashpot mechanism may be mechanical in nature rather than hydraulic, as should be understood. The external control of the dashpots enables the insulated tank to be optimally stabilized within the ship structure and not deleteriously affected by any rolling or pitching to which the ship may be subjected in a rough sea.

It will be appreciated that by utilizing the new and improved free-floating, dynamic support system hereinabove described, the cargo tank and its insulation will be free to expand and contract as a unit. This is of especially great importance, since the integrity of the insulation is enhanced and may best be preserved by permitting it to expand and contract freely, rather than by securing it directly to a fixed support. As should be understood, when the insulation is directly secured to a ship hull or similar support, there is a tendency to stress it unduly by restricting dimensional changes that would otherwise be effected by the large temperature gradients.

In accordance with the invention and as should be apparent from the foregoing, a multi-barrier cargo tank, which is to be cyclically subjected to alternate cryogenic and ambient temperatures and the accompanying severe thermal stresses induced thereby, may be efficiently and safely supported in a ship or like structure by isolating the tank from the structure in a flexible manner through dynamic support mechanisms. Preferably, this is accomplished by employing an isolating shell having slidably mounted dashpots to controllably accommodate relative displacements between the tank and the shell during the loading (chilling down) and unloading (warming up) cycle. Moreover, through the controlled regulation of the pressures in the dashpots, the tank itself may be selectively positioned within the shell and relative to the ship structure, as desired or found necessary, to optimize its stabilization.

It should be understood that the specific form of the invention herein illustrated and described is intended to be representative only, as certain changes may be made therein without departing from the clear teachings of the disclosure. Accordingly, reference should be made to the following appended claims in determining the full scope of the invention.

What is claimed is:

1. In a ship hull, a mounting system for a cryogenic cargo tank including 1 (a) a closed shell having three major axes,

(b) said shell being of predetermined substantially larger dimensions than said cargo tank,

(c) means rigidly securing said shell to said hull; channel members mounted exteriorly of said shell; dashpot means supported in said channel members for sliding motion relative along said shell; said shell defining openings adjacent said dashpot means,

((1) rod-like support means projecting through said openings; said support means connected at one end to said dashpot means,

(e) means adapted to secure the other end of said rodlike support means rigidly to said tank,

(f) whereby said tank may be effectively floatingly and universally displaceably supported within said shell.

I 2. The mounting system of claim 1, in which (a) a fluid pressure medium is supplied to said dashpot means, and

, (b) pressure control means for applying and controlling the pressure on said fluid pressure medium.

References Cited UNITED STATES PATENTS 2,922,622 7/1961 Maker.

3,016,160 1/1962 Scharpf 220-15 3,021,027 2/ 1962 Claxt0n 220-15 3,071,094 1/1963 Leroux 220-15 3,104,025 9/1963 Dosker 220-15 3,112,043 11/1963 Tucker 220-15 3,129,836 4/1964 Frevel 220-15 3,230,726 1/1966 Berner et al 62-45 THERON E. CONDON, Primary Examiner.

I. R. GARRETT, Assistant Exiaminer. 

1. IN A SHIP HULL, A MOUNTING SYSTEM FOR A CRYOGENIC CARGO TANK INCLUDING (A) A CLOSED SHELL HAVING THREE MAJOR AXES, (B) SAID SHELL BEING OF PREDETERMINED SUBSTANTIALLY LARGER DIMENSIONS THAN SAID CARGO TANK, (C) MEANS RIGIDLY SECURING SAID SHELL TO SAID HULL: CHANNEL MEMBERS MOUNTED EXTERIORLY OF SAID SHELL; DASHPOT MEANS SUPPORTED IN SAID CHANNEL MEMBERS FOR SLIDING MOTION RELATIVE ALONG SAID SHELL; SAID SHELL DEFINING OPENINGS ADJACENT SAID DASHPOT MEANS, (D) ROD-LIKE SUPPORT MEANS PROJECTING THROUGH SAID OPENINGS; SAID SUPPORT MEANS CONNECTED AT ONE END TO SAID DASHPOT MEANS, (E) MEANS ADAPTED TO SECURE THE OTHER END OF SAID RODLIKE SUPPORT MEANS RIGIDLY TO SAID TANK, 